A Red-Black tree based NavigableMap implementation.
The map is sorted according to the natural
ordering of its keys, or by a Comparator provided at map
creation time, depending on which constructor is used.

This implementation provides guaranteed log(n) time cost for the
containsKey, get, put and remove
operations. Algorithms are adaptations of those in Cormen, Leiserson, and
Rivest's Introduction to Algorithms.

Note that the ordering maintained by a tree map, like any sorted map, and
whether or not an explicit comparator is provided, must be consistent
with equals if this sorted map is to correctly implement the
Map interface. (See Comparable or Comparator for a
precise definition of consistent with equals.) This is so because
the Map interface is defined in terms of the equals
operation, but a sorted map performs all key comparisons using its
compareTo (or compare) method, so two keys that are deemed equal by
this method are, from the standpoint of the sorted map, equal. The behavior
of a sorted map is well-defined even if its ordering is
inconsistent with equals; it just fails to obey the general contract
of the Map interface.

Note that this implementation is not synchronized.
If multiple threads access a map concurrently, and at least one of the
threads modifies the map structurally, it must be synchronized
externally. (A structural modification is any operation that adds or
deletes one or more mappings; merely changing the value associated
with an existing key is not a structural modification.) This is
typically accomplished by synchronizing on some object that naturally
encapsulates the map.
If no such object exists, the map should be "wrapped" using the
Collections.synchronizedSortedMap
method. This is best done at creation time, to prevent accidental
unsynchronized access to the map:

SortedMap m = Collections.synchronizedSortedMap(new TreeMap(...));

The iterators returned by the iterator method of the collections
returned by all of this class's "collection view methods" are
fail-fast: if the map is structurally modified at any time after
the iterator is created, in any way except through the iterator's own
remove method, the iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent
modification, the iterator fails quickly and cleanly, rather than risking
arbitrary, non-deterministic behavior at an undetermined time in the future.

Note that the fail-fast behavior of an iterator cannot be guaranteed
as it is, generally speaking, impossible to make any hard guarantees in the
presence of unsynchronized concurrent modification. Fail-fast iterators
throw ConcurrentModificationException on a best-effort basis.
Therefore, it would be wrong to write a program that depended on this
exception for its correctness: the fail-fast behavior of iterators
should be used only to detect bugs.

All Map.Entry pairs returned by methods in this class
and its views represent snapshots of mappings at the time they were
produced. They do not support the Entry.setValue
method. (Note however that it is possible to change mappings in the
associated map using put.)

Constructor Detail

TreeMap

public TreeMap()

Constructs a new, empty tree map, using the natural ordering of its
keys. All keys inserted into the map must implement the Comparable interface. Furthermore, all such keys must be
mutually comparable: k1.compareTo(k2) must not throw
a ClassCastException for any keys k1 and
k2 in the map. If the user attempts to put a key into the
map that violates this constraint (for example, the user attempts to
put a string key into a map whose keys are integers), the
put(Object key, Object value) call will throw a
ClassCastException.

TreeMap

Constructs a new, empty tree map, ordered according to the given
comparator. All keys inserted into the map must be mutually
comparable by the given comparator: comparator.compare(k1,
k2) must not throw a ClassCastException for any keys
k1 and k2 in the map. If the user attempts to put
a key into the map that violates this constraint, the put(Object
key, Object value) call will throw a
ClassCastException.

Parameters:

comparator - the comparator that will be used to order this map.
If null, the natural
ordering of the keys will be used.

TreeMap

Constructs a new tree map containing the same mappings as the given
map, ordered according to the natural ordering of its keys.
All keys inserted into the new map must implement the Comparable interface. Furthermore, all such keys must be
mutually comparable: k1.compareTo(k2) must not throw
a ClassCastException for any keys k1 and
k2 in the map. This method runs in n*log(n) time.

containsValue

Returns true if this map maps one or more keys to the
specified value. More formally, returns true if and only if
this map contains at least one mapping to a value v such
that (value==null ? v==null : value.equals(v)). This
operation will probably require time linear in the map size for
most implementations.

get

Returns the value to which the specified key is mapped,
or null if this map contains no mapping for the key.

More formally, if this map contains a mapping from a key
k to a value v such that key compares
equal to k according to the map's ordering, then this
method returns v; otherwise it returns null.
(There can be at most one such mapping.)

A return value of null does not necessarily
indicate that the map contains no mapping for the key; it's also
possible that the map explicitly maps the key to null.
The containsKey operation may be used to
distinguish these two cases.

The set is backed by the map, so changes to the map are
reflected in the set, and vice-versa. If the map is modified
while an iteration over the set is in progress (except through
the iterator's own remove operation), the results of
the iteration are undefined. The set supports element removal,
which removes the corresponding mapping from the map, via the
Iterator.remove, Set.remove,
removeAll, retainAll, and clear
operations. It does not support the add or addAll
operations.

navigableKeySet

Returns a NavigableSet view of the keys contained in this map.
The set's iterator returns the keys in ascending order.
The set is backed by the map, so changes to the map are reflected in
the set, and vice-versa. If the map is modified while an iteration
over the set is in progress (except through the iterator's own
remove operation), the results of the iteration are undefined. The
set supports element removal, which removes the corresponding mapping
from the map, via the Iterator.remove, Set.remove,
removeAll, retainAll, and clear operations.
It does not support the add or addAll operations.

descendingKeySet

Returns a reverse order NavigableSet view of the keys contained in this map.
The set's iterator returns the keys in descending order.
The set is backed by the map, so changes to the map are reflected in
the set, and vice-versa. If the map is modified while an iteration
over the set is in progress (except through the iterator's own
remove operation), the results of the iteration are undefined. The
set supports element removal, which removes the corresponding mapping
from the map, via the Iterator.remove, Set.remove,
removeAll, retainAll, and clear operations.
It does not support the add or addAll operations.

values

The collection's iterator returns the values in ascending order
of the corresponding keys. The collection's spliterator is
late-binding,
fail-fast, and additionally reports Spliterator.ORDERED
with an encounter order that is ascending order of the corresponding
keys.

The collection is backed by the map, so changes to the map are
reflected in the collection, and vice-versa. If the map is
modified while an iteration over the collection is in progress
(except through the iterator's own remove operation),
the results of the iteration are undefined. The collection
supports element removal, which removes the corresponding
mapping from the map, via the Iterator.remove,
Collection.remove, removeAll,
retainAll and clear operations. It does not
support the add or addAll operations.

The set is backed by the map, so changes to the map are
reflected in the set, and vice-versa. If the map is modified
while an iteration over the set is in progress (except through
the iterator's own remove operation, or through the
setValue operation on a map entry returned by the
iterator) the results of the iteration are undefined. The set
supports element removal, which removes the corresponding
mapping from the map, via the Iterator.remove,
Set.remove, removeAll, retainAll and
clear operations. It does not support the
add or addAll operations.

descendingMap

Returns a reverse order view of the mappings contained in this map.
The descending map is backed by this map, so changes to the map are
reflected in the descending map, and vice-versa. If either map is
modified while an iteration over a collection view of either map
is in progress (except through the iterator's own remove
operation), the results of the iteration are undefined.

The returned map has an ordering equivalent to
Collections.reverseOrder(comparator()).
The expression m.descendingMap().descendingMap() returns a
view of m essentially equivalent to m.

subMap

Returns a view of the portion of this map whose keys range from
fromKey to toKey. If fromKey and
toKey are equal, the returned map is empty unless
fromInclusive and toInclusive are both true. The
returned map is backed by this map, so changes in the returned map are
reflected in this map, and vice-versa. The returned map supports all
optional map operations that this map supports.

The returned map will throw an IllegalArgumentException
on an attempt to insert a key outside of its range, or to construct a
submap either of whose endpoints lie outside its range.

fromInclusive - true if the low endpoint
is to be included in the returned view

toKey - high endpoint of the keys in the returned map

toInclusive - true if the high endpoint
is to be included in the returned view

Returns:

a view of the portion of this map whose keys range from
fromKey to toKey

Throws:

ClassCastException - if fromKey and toKey
cannot be compared to one another using this map's comparator
(or, if the map has no comparator, using natural ordering).
Implementations may, but are not required to, throw this
exception if fromKey or toKey
cannot be compared to keys currently in the map.

NullPointerException - if fromKey or toKey is
null and this map uses natural ordering, or its comparator
does not permit null keys

IllegalArgumentException - if fromKey is greater than
toKey; or if this map itself has a restricted
range, and fromKey or toKey lies
outside the bounds of the range

Since:

1.6

headMap

Returns a view of the portion of this map whose keys are less than (or
equal to, if inclusive is true) toKey. The returned
map is backed by this map, so changes in the returned map are reflected
in this map, and vice-versa. The returned map supports all optional
map operations that this map supports.

The returned map will throw an IllegalArgumentException
on an attempt to insert a key outside its range.

inclusive - true if the high endpoint
is to be included in the returned view

Returns:

a view of the portion of this map whose keys are less than
(or equal to, if inclusive is true) toKey

Throws:

ClassCastException - if toKey is not compatible
with this map's comparator (or, if the map has no comparator,
if toKey does not implement Comparable).
Implementations may, but are not required to, throw this
exception if toKey cannot be compared to keys
currently in the map.

NullPointerException - if toKey is null
and this map uses natural ordering, or its comparator
does not permit null keys

tailMap

Returns a view of the portion of this map whose keys are greater than (or
equal to, if inclusive is true) fromKey. The returned
map is backed by this map, so changes in the returned map are reflected
in this map, and vice-versa. The returned map supports all optional
map operations that this map supports.

The returned map will throw an IllegalArgumentException
on an attempt to insert a key outside its range.

inclusive - true if the low endpoint
is to be included in the returned view

Returns:

a view of the portion of this map whose keys are greater than
(or equal to, if inclusive is true) fromKey

Throws:

ClassCastException - if fromKey is not compatible
with this map's comparator (or, if the map has no comparator,
if fromKey does not implement Comparable).
Implementations may, but are not required to, throw this
exception if fromKey cannot be compared to keys
currently in the map.

NullPointerException - if fromKey is null
and this map uses natural ordering, or its comparator
does not permit null keys

subMap

Returns a view of the portion of this map whose keys range from
fromKey, inclusive, to toKey, exclusive. (If
fromKey and toKey are equal, the returned map
is empty.) The returned map is backed by this map, so changes
in the returned map are reflected in this map, and vice-versa.
The returned map supports all optional map operations that this
map supports.

The returned map will throw an IllegalArgumentException
on an attempt to insert a key outside its range.

a view of the portion of this map whose keys range from
fromKey, inclusive, to toKey, exclusive

Throws:

ClassCastException - if fromKey and toKey
cannot be compared to one another using this map's comparator
(or, if the map has no comparator, using natural ordering).
Implementations may, but are not required to, throw this
exception if fromKey or toKey
cannot be compared to keys currently in the map.

NullPointerException - if fromKey or toKey is
null and this map uses natural ordering, or its comparator
does not permit null keys

IllegalArgumentException - if fromKey is greater than
toKey; or if this map itself has a restricted
range, and fromKey or toKey lies
outside the bounds of the range

headMap

Returns a view of the portion of this map whose keys are
strictly less than toKey. The returned map is backed
by this map, so changes in the returned map are reflected in
this map, and vice-versa. The returned map supports all
optional map operations that this map supports.

The returned map will throw an IllegalArgumentException
on an attempt to insert a key outside its range.

a view of the portion of this map whose keys are strictly
less than toKey

Throws:

ClassCastException - if toKey is not compatible
with this map's comparator (or, if the map has no comparator,
if toKey does not implement Comparable).
Implementations may, but are not required to, throw this
exception if toKey cannot be compared to keys
currently in the map.

NullPointerException - if toKey is null
and this map uses natural ordering, or its comparator
does not permit null keys

tailMap

Returns a view of the portion of this map whose keys are
greater than or equal to fromKey. The returned map is
backed by this map, so changes in the returned map are
reflected in this map, and vice-versa. The returned map
supports all optional map operations that this map supports.

The returned map will throw an IllegalArgumentException
on an attempt to insert a key outside its range.

a view of the portion of this map whose keys are greater
than or equal to fromKey

Throws:

ClassCastException - if fromKey is not compatible
with this map's comparator (or, if the map has no comparator,
if fromKey does not implement Comparable).
Implementations may, but are not required to, throw this
exception if fromKey cannot be compared to keys
currently in the map.

NullPointerException - if fromKey is null
and this map uses natural ordering, or its comparator
does not permit null keys